For about two decades, immunoassay procedures have provided sensitive diagnostic tools for the in vitro detection of a variety of antigens associated with disease or other physical conditions of clinical significance. Originally such heterogeneous assays used a polyclonal antibody preparation bound to a solid phase. In these assays, a solution of labeled antigen is allowed to compete directly with antigen in the sample being analyzed for the solid phase antibody or is added to the antibody in a sequential process. The extent to which the labeled antigen is bound to the solid phase or is detected in the liquid phase can be used as a measure of the presence and quantity of antigen in the sample being analyzed.
Subsequently, non-competitive immunometric assays became available. In these assays, a polyclonal antibody preparation bound to a solid phase was also used. The sample containing the suspected antigen was allowed to contact the solid phase in order for the antigen to bind to the antibodies on the solid phase. Typically, after an incubation step the sample was separated from the solid phase which was then washed and incubated with a solution of additional polyclonal antibodies which had been labeled, for example with a radionuclide, an enzyme, or a fluorescent moiety.
After this second incubation, the unbound labeled antibody was separated from the solid phase and the amount of labeled antibody in either the liquid phase or bound to the solid phase in an antibody:antigen:antibody sandwich was determined as a measure of the presence and/or concentration of antigen in the sample tested.
More recently, immunoassay procedures have been modified to use monoclonal antibodies. For example, U.S. Pat. No. 4,376,110 describes two-sit immunometric assays using pairs of monoclonal antibodies, one bound to a solid phase and the other labeled to permit detection. The use of monoclonal antibody pairs which recognize different epitopic sites on an antigen has made it possible to conduct simultaneous immunometric assays in which the antigen and labeled antibody incubations do not require the intermediate washing steps of prior processes.
In the foregoing processes, the solid phase antibody is typically bound to a bead or small particles or coated on a surface. Alternatively, microspheres to which are bound antibody may be entrapped within a porous matrix. Recent improvements have drastically reduced the time necessary for the performance of the assays. As a result simpler and more rapid procedures for conducting immunoassays which employ a relatively simple apparatus make such assays available for use in the physician's office and even for over-the-counter sale to lay persons for use in home health care programs. For example, U.S. Pat. No. 3,811,840 describes a test device for detecting low concentrations of substances in test fluids comprising an adsorbant wick having a substantially flat surface portion enclosed in a fluid impervious sheath having an aperture of predetermined limited area formed therein. The aperture being contiguous to and exposing a predetermined limited area of the flat surface portion of the wick area. Within this aperture portion of the wick is incorporated a reagent specifically reactable with the substance being detected. In use, the device is dipped into the test fluid where the test fluid contacts the reagent area of the aperture and migrates into the remainder of the wick. Also, U.S. Pat. No. 4,366,241 discloses an apparatus provided for performing immunoassays employing a device consisting of a relatively small test zone referred to as an immunoabsorbing zone, and a relatively large liquid adsorbing zone in liquid receiving relationship with the immunoabsorbing zone. At least a portion of the liquid adsorbing member about the immunoabsorbing zone is enclosed in an impermeable enclosure. Presently available from Hybritech Incorporated is a product sold under the trademark ICON.RTM.. It is described in detail in G. Valkirs, et al., Ser. No. 609,395, filed May 11, 1984, now U.S. Pat. No. 4,632,901, issued Dec. 30, 1986, and its continuation-in-part, Ser. No. 733,292, filed May 10, 1985, now U.S. Pat. No. 4,727,019, issued Feb. 23, 1988. The product employs a device which comprises a membrane having antibody fixed to its surface in conjunction with an absorbent member. The two components are enclosed in a container open at one end to permit sample to be applied to the membrane. The absorbent member, in capillary contact with the membrane, draws liquid through the membrane after it is applied. Air displaced within the body of the container by the addition of liquid passes through small ports located, for example, near the bottom of the container.
It is important that the moisture sensitive components of an apparatus for conducting immunoassays be protected from contact with contaminating moisture prior to use. A method presently used is to place the Hybritech Incorporated ICON.RTM. product, referred to above, within a hermetically sealed pouch containing desiccants well known in the art. This particular method, although well suited for its particular purposes, is expensive, adds complexity to the packaging of the apparatus, and increases the size of the packaged product. Accordingly, an apparatus for conducting immunoassays which can be simply sealed from contaminating moisture would be desirable.